Heretofore there have been trucks having independently movable side frames, air springs supporting a car body on a bolster, a bolster turnably supported on side frames, said wheel-axle units having resilient bearing connections with the side frames.
One such truck having these characteristics was the "Pioneer" truck, U.S. Pat. No. 2,908,230, which, in various models, has such characteristics and has been extensively used for many years in both local and main line operation and has given economical and safe service over long periods of time with minimal attention.
Also there have been trucks having transom bars rigid with one side frame and having joint connections with the other side frame which provide universal movements, as through elastomeric connections or ball joints. For example, see U.S. Pat. No. 2,879,718.
However, so far as known, there have been no trucks of this type which provided the improvement in ride performance and control secured by the present invention. In particular, as a detail, the universal joints of the transom bars did not give positive control of truck tram.